Hey Zizirimu-
Not really one to speak on the canon and lore aspect- as I'm new to it myself and -really- don't know anything about Lala history (as I will not be playing one- but hope to gain a strong understanding of all the Eorzean cultures via RP and directed research)...
But I found your storyline idea to be rather interesting and creative.
My only concern would be a word of caution to not make A'zizi -too- good at everything that he becomes a Gary Lou (or whatever the male version of the Mary Sue is.. haha).
I think linking a bio of him would be good- one that lists his strengths, weaknesses, etc- so that readers of the above could get a more complete understanding of who he is- not just the legend.
If you DO plan to make him some sort of Bright One reborn... cool... but just make him relate-able too. Give him areas in which he can grow/develop, frailties and so forth.
It seems from my reading of threads here, and the wiki, that the FF universe is quite large and forgiving of unique/unusual takes on things and events- so it =seems= your idea could work... especially if you have a good RP story to explain things and, as I said before, ensure he's not "Super Lala".